Automatic transmissions are known in which a movable element is driven in accordance with the pressure of a fluid supplied to the movable element and the transmission gear ratio is thereby changed, as exemplified by stepped transmissions in which a friction element as a movable element is engaged or disengaged in accordance with the pressure of a fluid supplied to the movable element and the transmission gear ratio is thereby changed stepwise.
To control a fluid to be supplied to the movable element, automatic transmissions employ a fluid circuit module as disclosed in U.S. Pat. No. 6,308,725, for example. Usually, in fluid circuit module products, a pressure regulating valve means for adjusting the pressure of a fluid to be supplied to the movable element and a pressure sensor for detecting the pressure of, for example, the fluid to be supplied to the movable element are incorporated in a body that forms a flow passage. In such fluid circuit modules, the operation of the pressure regulating valve means is controlled on the basis of a detection result of the pressure sensor and a fluid to be supplied to the movable element is thereby controlled.
However, in fluid circuit modules used for automatic transmissions, the pressure of a fluid to be handled is high and the pressure sensor is necessarily large. Therefore, the pressure sensor projects outward from the body, as a result of which not only the size of the fluid circuit module but also the size of the automatic transmission is large. In addition, to detect a pressure difference between plural flow passages and flow rates of the respective flow passages, plural such large-size pressure sensors need to be provided. In this case, the sizes of the fluid circuit module and the automatic transmission are further increased.